Photoshop TIFF: fix offset to first layer

Fixes #10203.
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 347 (Photoshop TIFF: fix offset to first layer (rebased onto develop))
merge develop -D org -I include -E conflict -E needs-fixes -E broken

Repository: openmicroscopy/bioformats
Already up-to-date.
Merged PRs:
  # PR 347 melissalinkert 'Photoshop TIFF: fix offset to first layer (rebased onto develop)'

Generated by SCC-merge#123 (http://hudson.openmicroscopy.org.uk/job/SCC-merge/123/)